Mark Jaquith

This plugin allows you to customize the logo on the WordPress login screen. There is zero configuration. You just drop the logo file into your WordPress content directory, named <code>login-logo.png</code> and this plugin takes over.
Note that you should use a transparent background on the PNG image, crop it tightly (no padding pixels) and use a width of exactly 312 pixels for best results. Wider images will be downscaled in modern browsers, but it isn’t recommended to rely on that.
This plugin also works in the <code>mu-plugins</code> directory.

Login Logo

Customize the logo on the WP login screen by simply dropping a file named login-logo.png into your WP content directory. CSS is automatic!

Scott DeLuzio

AMP-MODE

WordPress Login Logo Editor is a plugin that easily lets you edit the form and logo shown when logging into your WordPress site. WordPress Login Logo Editor allows you to edit:
<ul>
<li>The image above the login form on your WordPress site.</li>
<li>The URL that a user gets directed to when the logo is clicked. By default you are directed to http://wordpress.org.</li>
<li>The title text that appears when your mouse hovers over the login logo. By default this text says Powered by WordPress.</li>
<li>Style the login window with custom CSS.</li>
</ul>

Login Logo Editor

Easily lets you edit the form and logo shown when logging into your WordPress site.

Login Logo vs Login Logo Editor